It is well known that a turbo-type vacuum pump comprises an external housing with gas pumping stages housed therein.
The gas pumping stages are generally formed by the arrangement of stator rings integral to the pump body and rotor disks integral to a rotating shaft operated by a motor of the pump.
The rotor disks can be flat disks or be provided with slanting fins.
There are vacuum pumps, generally the turbo-molecular ones, that comprise both flat disks and disks having fins. These pumps allow to obtain pressures of approximately 10.sup.-8 Pa, with very high rotating speeds reaching 100.000 revolutions per minute.
A shaft of the pump rotor and a shaft of the motor normally coincide in one rotating shaft, supported by appropriate rotation supporting means.
Generally the shaft is supported by bearings that can be roller bearings, having balls or rolls, or magnetic bearings. The bearings provide a free rotation and a precise balancing of the shaft.
One type of a conventional vacuum pump is provided with a pair of roller bearings placed on the rotating shaft between the electric motor and the pumping section. Though such configuration has a simple construction and easy maintenance, the motor, the bearings and the pumping section are completely separated there between, which does not allow to manufacture the pumps having compact dimensions, especially in the axial direction.
Another type of a turbo molecular vacuum pump, axially more compact than that described above, is disclosed in the U.S. Pat. No. 5,165,872. The '872 Patent teaches a vacuum pump having a bell-shaped integral pumping rotor having a cylindrical cavity with an electric motor and bearings housed therein in addition to a rotating shaft of a pumping rotor. The motor of this vacuum pump is placed between the bearings and its shaft coincides with the rotating shaft of the pump.
The second type of the turbo-molecular pump is more compact compared to the first one. However, the distance between bearings can never be smaller than the length of the motor.